Unity - The multiplatform game creation tools for everyone.
Sampulator - Make (and record) beats on your keyboard
Godot Engine - Feature-packed 2D and 3D open source game engine.
Auxy Music Studio - Auxy brings real music creation to iPhone in a simple and inspiring format.
Blender - Blender is the open source, cross platform suite of tools for 3D creation.
Ramsophone - A generative art/music machine. (Be sure to refresh!)